Recently, high-speed input-output buffer has been required as high-speed LSI is developed. Such a high-speed input-output buffer is realized by lowering the amplitude of signal. Especially, for input buffer, differential circuit is frequently used to obtain noise margin. On the other hand, IDDQ test to check the leakage current of LSI is a useful method for LST test, and is increasingly in demand.
Conventionally, for LSI which uses a differential circuit where the short-circuit current cannot be cut off, the IDDQ test is conducted adding part of short-circuit current. However, since the part of short-circuit current is significantly greater than the leakage current to flow in case of fault, there is a problem that it is difficult to know which the current measured is leakage current or short-circuit current. Also, when the short-circuit current is cut off by stopping the operation of differential circuit using input enable terminal, it is difficult to give a test pattern with high fault coverage for LSI internal circuit, since the logic output from input buffer circuit is fixed.